Pulverizing mills

HERZOG offers a wide range of pulverizimg mills - From manual machines to fully automatic laboratory automation.

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HSM 50: Manual pulverizing mill

Material feed size: < 10 mm
Feed volume: 50 ccm, 10 ccm
Manual sample preparation and cleaning

HSM 100/ HSM 250: Manual pulverizing mill

Material feed size: <10 mm
Feed volume: 100 ccm, 250 ccm, 10 ccm, 50 ccm
Manual sample preparation and cleaning

HP-M 100P: Semi-automatic pulverizing mill

Material feed size: < 5 mm
Feed volume: 100 ccm
Manual sample input, automatic sample discharge and cleaning

HP- M 5000: Automatic pulverizing mill

Material feed size: <5 mm
Feed volume: 5000 ccm
Fully automatic sample preparation

HERZOG expertise in pulverizing

The grinding process is a time- and cost-saving sample preparation procedure that is used in the analysis of many inorganic and organic materials. HERZOG supplies an extensive product range for this type of sample preparation, extending from manual machines to fully automatic laboratory automations. Using powdered samples not only allows the chemical composition to be determined, it also permits the use of X-ray diffraction methods (e.g. cement, salts) for some applications in order to determine the mineral content.

DetailTo pulverizers

Milling process

Prior to pressing, the material must be finely ground in order to guarantee sufficient homogeneity. HERZOG offers a wide variety of vibration mills in different sizes and configurations for the grinding of sample material. Very hard materials (e.g. silicon carbide) can also be ground down to a grain size that is sufficiently fine to guarantee a high-quality analysis. Along with the program parameters, the attainable fineness is also dependent on the following factors:

  • Material
  • Input quantity
  • Grinding aids used
  • Grain size when put in

To perform the analysis by means of XRF, it is often necessary for the sample material to be ground to a grain size of < 75 μm. The grinding vessels must be made from wear-resistant materials in order to guarantee sufficient abrasion resistance. This applies particularly when the sample contains very hard mineral phases and has abrasive properties (e.g. clinker, silicon carbide, etc.). This means that during grinding, there is inevitably abrasion of the used grinding stones and of the grinding vessel. Depending on the application, the grinding vessel should be suitably hard and should have a chemical composition
that does not contain any elements that are of analytical interest. Different grinding vessels are available in order to prevent the entry of elements that are relevant to the analysis.

Configuration of the grinding vessel

Generally, there are four grinding vessel volumes available for grinding with manual mills (10, 50, 100 and 250 cm³). Only 100 cm³ grinding vessels are used in the case of automatic mills. If smaller grinding vessels are used in larger holders, intermediate rings and spacers can be used as adapters. The required components are shown together in Figure 1 for the mill types HSM 250 H/HSM 250 P and HSM 100 H/HSM 100 P. The maximum speed of these mill types is 1470 rpm. Various combinations of rings and stones are employed as grinding tools. In grinding vessels with a volume of between 10 and 50 cm³, only a single stone is used to grind the sample material. A combination of a ring and a stone is used in the 100 cm³ grinding vessel. Two rings and a stone are used in order to guarantee sufficient pulverization
in the 250 cm³ grinding vessel as well. Agate grinding vessels are available with a volume of 100 cm³. However, due to their brittle character, agate grinding vessel can only be used with a maximum grinding speed of 750 rpm.

Mills and press types

For sample preparation, there are different mill and press models that can be optionally fitted with various extensions in order to meet the needs of the sample preparation and automation complexity. A distinction can be made between the following mill types:
• Manual mills: HSM 50, HSM 100 H, HSM 100 P, HSM 100 A, HSM 250 H, HSM 250 P
• Automatic mills: HP-M, HP-MS, HP-MA.

The HP-MP, in which the advantages of a mill and a press have been combined in one machine, is a special case. This is particularly advantageous in laboratories where only limited space is available. With manual mills, the grinding vessel must be filled, emptied and cleaned manually. With automatic mills, this is done without the operator’s intervention. Optionally, automatic mills can be equipped with additional functions in order to increase the reproducibility of sample processing and to prevent contamination between the samples.

With automatic mills, there is a choice between the following options:
• Spoon dosing (defines input quantity and allows blank sample)
• Pill dosing (precise dosing of grinding tablets)
• Sand cleaning (use of quartz sand or other abrasive materials)
• Wet cleaning (using water and additives).
Automatic mills with input magazines also provide the possibility of batch processing. With this, several sample cups belonging to a sample batch can be ground without cleaning being done between each sample run. Besides minimising the preparation time, this also helps to reduce possible material losses.

 

 


Overview of the various milling machines showing their possible configurations and options

Grinding aids

Grinding aids have many different functions in the crushing of sample material. Grinding aids are particularly used with samples that have components with different grinding properties. The amount of grinding aid used depends on the application and is usually between 2 % and 10 % of the sample quantity. Too much grinding aid results in intensities decrease and increases the detection limits of
the analysis. Since just-pressed samples are used for the analysis of trace elements, dilution effects in the sample preparation play a decisive role. During pressing, the grinding aid tablets can be used in order to obtain a stable pellet. This is particularly necessary for materials. The use of grinding aid tablets containing wax offers the additional advantage that moisture absorption is reduced.

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